26-31 Musci Feature

ITE JOURNAL / JANUARY 2003 INTRODUCTION Approaches to combat urban traffic congestion span from demand management to physical expansion of road capacity. Attempts to shift a part of peak travel from car to high-quality public transit and to times when roads are relatively less crowded sometimes have been successful.1,2 Also, intelligent transportation systems (ITS) have the promise to optimize the operation of transportation systems and delay the building of additional lanes.3 However, the most common attempt to alleviate traffic congestion at intersections is to provide more road space to vehicles.4 Since very little or no research exists on the optimum size of intersections, they are often made as large as traffic demand projections require and/or the available rightof-way (ROW) allows. It is often assumed that this approach is both an effective and a sustainable way to provide for growing travel demand. From the technical perspective, increasing the number of lanes could be a sustainable approach to satisfy traffic demand only if the marginal capacity of additional lanes can match the marginal traffic demand increase. This feature shows that the effectiveness of additional lanes decreases as the size of the intersection increases. Effectiveness is expressed in terms of marginal capacity increase of the additional lanes, vehicle delay and queue lengths. Typical urban intersections usually are expanded a number of times during a 60to 80-year span. Evaluating and comparing the operation of a particular intersection during this period is technically infeasible due to changes in the environment and the lack of appropriate historical data. In this feature, measures of effectiveness (MOEs) of a hypothetical intersection during a similar life span are evaluated and compared assuming common traffic engineering procedures are applied as traffic demand grows. The authors appreciate that adding new traffic lanes is often the only feasible approach to reduce congestion in the short term. However, the objective of the feature is to demonstrate technical reasons why this approach is not sustainable in the long run.